The combined effect of limited water resources and ever-growing water demand necessitates the use of more-accurate approaches for reservoir water-balance analyses. Therefore, this study aims to develop a new operational scheme by considering flood control and variations in irrigation efficiency for simulating reservoir water-balance components. This study is conducted on three reservoirs in Korea, which were monitored for 4 years. Based on the findings of the sensitivity analyses, irrigation efficiency variation appears to be most sensitive to the outflow variables and was thus calibrated on a yearly basis. Compared with the two other schemes, i.e., with respective exclusions of flood control and irrigation efficiency variations, the new scheme performs better in simulating reservoir water levels. Additionally, it is found that without the consideration of the newly developed scheme, significant errors could occur in the simulation of water-balance components, which could lead to incorrect decisio...